WORK AND

POWER

Work Work – the product of force

and the distance traveled The unit of Work is a Joule

(J)

Work= Force × distanceW = F ● dDistance (m)Force (N)

Work (joules)

Which would be more work?

Pushing a Crate 10 feet?

OR Pushing a Crate 100 feet?

Calculate Work During the ascent phase of a rep of the

bench press, the lifter exerts an average vertical force of 1000 N against a barbell while the barbell moves 0.8 m upward. How much work did the lifter do to the barbell?

Force = Distance = Work =

1000 N 0.8 m(1000 N) × (0.8 m) = 800 joules

Calculate Work Calculate the work needed to

push a block with 4 newtons of force a distance of 10 meters.

Force = Distance = Work =

4 N10 m

(4 N) × (10 m) = 40 joules

Calculate Work An automobile engine exerts a

force of 500 newtons on a car to travel 4,000 meters. What is the amount of work done by the engine?

Force = Distance = Work =

500 N 4,000

m(500 N) × (4,000 m) = 2,000,000 joules

Power Power – the rate of doing work

The Unit of Power is a Watt (W)

Power = Work time (in seconds)

P = W same as P = F • d t t

Who is more Powerful?

He-Man who can push a crate 100 feet in 1 second using 5 Newtons?

OR Skeletor, who can push a crate 100 feet in 45 seconds

using 5 Newtons?

1 second

45 seconds

Calculate Power How much power is necessary

to do 50 joules of work in 5 seconds?

Work = Time = Power =

50 joules 5 s

(50 J) ÷ (5 s) = 10 watt

Calculate Power An electrical water heater raises the

temperature of water by adding 8,000 joules of energy to the water in 40 seconds. What is the minimum power required by the water heater?

Work = Time = Power =

8,000 joules40 s(8,000 J) ÷ (40 s) = 200 watt

Calculate Power Jake, who weighs 680 newtons,

climbs a 6 meter ladder in 8 seconds. What was Jake’s power?

Force = Distance = Work = Time = Power =

680 N 6 m

(680N) × (6 m) = 4,080 joules8 s(4,080 J) ÷ (8 s) = 510 watt

Complete WS practice problems

You may listen to music Work quietly, do NOT talk! Turn it in when complete Finish in class, homework

if you do not finish in class.